1. Field of the Invention
This invention relates generally to a bone graft delivery system for a vertebral interbody device and, more particularly, to a bone graft delivery system for a vertebral interbody device that includes an auger for delivering the bone graft material from a hopper to the interbody device to be disbursed within the vertebral disc space.
2. Discussion of the Related Art
The human spine includes a series of vertebrae interconnected by connective tissue referred to as disks that act as a cushion between the vertebrae. The disks allow for movement of the vertebrae so that the back can bend and rotate.
Spinal fusion is a surgical procedure that fuses two or more vertebrae together using bone grafts and/or other devices. Spinal fusion is a commonly performed procedure for the treatment of chronic neck and back pain refractory to non-operative treatments. Spinal fusion is used to stabilize or eliminate motion of vertebrae segments that may be unstable, i.e., move in an abnormal way, that may lead to pain and discomfort. Spinal fusion is typically performed to treat injuries to the vertebrae, degeneration of the spinal disks, abnormal spinal curvature and a weak or unstable spine.
In an attempt to preserve normal anatomical structures during spine surgery, minimally invasive surgical procedures have been devised. One such procedure involves the use of a series of muscle dilators that separate the muscle fibers of the spine to create a pathway to the spine. A Kirschner (K-wire) is initially introduced through a small incision and directed towards the spinal pathology. The position of the K-wire is visualized by a fluoroscopic imaging system to identify its location. An initial narrow diameter muscle dilator is passed over the K-wire, and the K-wire is removed and subsequent larger muscle dilators are continually passed. When the opening is large enough, an access tube or retractor is positioned around the last muscle dilator through which the surgery is performed. The inner sequential muscle dilators are then removed allowing the surgeon to operate through the tubular retractor. The retractors come in a variety of lengths and diameters for different patients and procedures.
Spinal fusion generally requires a graft material, usually bone material, to fuse the vertebrae together. The bone graft material can be placed over the spine to fuse adjacent vertebrae together. Alternatively, a cage is positioned between the vertebrae being fused, and is filled with the graft material. This procedure is referred to as interbody fusion since it is between adjacent vertebra. The cage includes holes that allow the vertebra and the graft material to grow together to provide the fusion. The cage supports the weight of adjacent vertebra while the fusion is occurring through the cage. Alternatively, the bone graft material can be placed directly over or lateral to the spine, referred to as postero-lateral fusion. Typically the bone graft material is autogenous bone material taken from the patient, or allograft bone material harvested from cadavers. Synthetic bone materials can also be used as the graft material. Generally, the patient's own bone material offers the best fusion material and is the current “gold standard”.
Spinal instrumentation is then performed to immobilize the vertebral segments where the bone is placed. Similar to the function of wearing a cast or brace after breaking a long bone, spinal instrumentation allows for immobilization, which promotes bone fusion. One of the most common forms of spinal instrumentation is a pedicle screw and rod construct. The rods, which span adjacent vertebra, are mounted to the vertebra using pedicle screws that are threaded through the pedicles of each vertebra and into the vertebral body. Accurate placement of the pedicle screws relative to the vertebral pedicle is very important to prevent injury to nerves or spinal cord. Typically, fluoroscopy is used to ensure that the pedicle screws are properly oriented relative to the pedicle.
During spinal fusion surgical procedures, it is necessary to completely remove the disc and clean out the disc space between the vertebra being fused. Particularly, it is necessary to remove as much of the disc material as possible between the vertebra so that the graft material that will be provided between the vertebra for the fusion provides a good bone-to-bone adhesion. Any remaining disc material that is not removed reduces the chance that the graft material will provide the bone graft adhesion necessary for a satisfactory fusion process.
Currently, various surgical devices are used in the art to remove the disc material for both minimally invasive and open spinal fusion procedures. For minimally invasive spinal surgery, a cutting device, such as a pituitary rongeur, is used to remove the disc material. The pituitary rongeur is a mechanical device including a “cup end” that cuts and scoops out the disc material to remove it in a mechanical operation. Manipulating the cup end of the pituitary rongeur is relatively cumbersome in that it is limited in its ability to clear the disc space around corners and other “guarded” areas proximate to the vertebrae. Further, because the pituitary rongeur is a mechanical device, it is limited in its ability to protect sensitive parts of the vertebrae, such as spinal nerves running through the disc space.